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Subject: Re: Too large badblocks sysfs file (was: [PATCH v3 0/7] badblocks
 improvement for multiple bad block ranges)
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, linux-block@vger.kernel.org,
        linux-raid@vger.kernel.org, nvdimm@lists.linux.dev,
        antlists@youngman.org.uk, Dan Williams <dan.j.williams@intel.com>,
        Hannes Reinecke <hare@suse.de>, Jens Axboe <axboe@kernel.dk>,
        NeilBrown <neilb@suse.de>, Richard Fan <richard.fan@suse.com>,
        Vishal L Verma <vishal.l.verma@intel.com>, rafael@kernel.org
References: <20210913163643.10233-1-colyli@suse.de>
 <a0f7b021-4816-6785-a9a4-507464b55895@suse.de> <YUwZ95Z+L5M3aZ9V@kroah.com>
From:   Coly Li <colyli@suse.de>
Message-ID: <e227eb59-fcda-8f3e-d305-b4c21f0f2ef2@suse.de>
Date:   Thu, 23 Sep 2021 14:14:12 +0800
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On 9/23/21 2:08 PM, Greg Kroah-Hartman wrote:
> On Thu, Sep 23, 2021 at 01:59:28PM +0800, Coly Li wrote:
>> Hi all the kernel gurus, and folks in mailing lists,
>>
>> This is a question about exporting 4KB+ text information via sysfs
>> interface. I need advice on how to handle the problem.

Hi Greg,

This is the code in mainline kernel for quite long time.

> Please do not do that.  Seriously, that is not what sysfs is for, and is
> an abuse of it.
>
> sysfs is for "one value per file" and should never even get close to a
> 4kb limit.  If it does, you are doing something really really wrong and
> should just remove that sysfs file from the system and redesign your
> api.

I understand this. And what I addressed is the problem I need to fix.

The code is there for almost 10 years, I just find it during my work on 
bad blocks API fixing.


>
>> Recently I work on the bad blocks API (block/badblocks.c) improvement, there
>> is a sysfs file to export the bad block ranges for me raid. E.g for a md
>> raid1 device, file
>>      /sys/block/md0/md/rd0/bad_blocks
>> may contain the following text content,
>>      64 32
>>     128 8
> Ick, again, that's not ok at all.  sysfs files should never have to be
> parsed like this.

I cannot agree more with you. What I am asking for was ---- how to fix it ?

Thanks.

Coly Li